Method and device for separating hydrocarbons and contaminants with a heating mechanism to destabilize and/or prevent adhesion of solids

ABSTRACT

The present disclosure provides a method for separating a feed stream in a distillation tower which includes separating a feed stream in a stripper section into an enriched contaminant bottom liquid stream and a freezing zone vapor stream; contacting the freezing zone vapor stream in the controlled freeze zone section with a freezing zone liquid stream at a temperature and pressure at which a solid and a hydrocarbon-enriched vapor stream form; directly applying heat to a controlled freeze zone wall of the controlled freeze zone section with a heating mechanism coupled to at least one of a controlled freeze zone internal surface of the controlled freeze zone wall and a controlled freeze zone external surface of the controlled freeze zone wall; and at least one of destabilizing and preventing adhesion of the solid to the controlled freeze zone wall with the heating mechanism.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of U.S. patent applicationNo. 61/912,986 filed Dec. 6, 2013 entitled METHOD AND DEVICE FORSEPARATING HYDROCARBONS AND CONTAMINANTS WITH A HEATING MECHANISM TODESTABILIZE AND/OR PREVENT ADHESION OF SOLIDS, the entirety of which isincorporated by reference herein.

This application is related to but does not claim priority to U.S.Provisional patent application Nos. 61/912,957 filed Dec. 6, 2013entitled METHOD AND DEVICE FOR SEPARATING HYDROCARBONS AND CONTAMINANTSWITH A SPRAY ASSEMBLY; 62/044,770 filed Sep. 2, 2014 entitled METHOD ANDDEVICE FOR SEPARATING HYDROCARBONS AND CONTAMINANTS WITH A SPRAYASSEMBLY; 61/912,959 filed on Dec. 6, 2013 entitled METHOD AND SYSTEM OFMAINTAINING A LIQUID LEVEL IN A DISTILLATION TOWER; 61/912,964 filed onDec. 6, 2013 entitled METHOD AND DEVICE FOR SEPARATING A FEED STREAMUSING RADIATION DETECTORS; 61/912,970 filed on Dec. 6, 2013 entitledMETHOD AND SYSTEM OF DEHYDRATING A FEED STREAM PROCESSED IN ADISTILLATION TOWER; 61/912,975 filed on Dec. 6, 2013 entitled METHOD ANDSYSTEM FOR SEPARATING A FEED STREAM WITH A FEED STREAM DISTRIBUTIONMECHANISM; 61/912,978 filed on Dec. 6, 2013 entitled METHOD AND SYSTEMFOR PREVENTING ACCUMULATION OF SOLIDS IN A DISTILLATION TOWER;61/912,983 filed on Dec. 6, 2013 entitled METHOD OF REMOVING SOLIDS BYMODIFYING A LIQUID LEVEL IN A DISTILLATION TOWER; 61/912,984 filed onDec. 6, 2013 entitled METHOD AND SYSTEM OF MODIFYING A LIQUID LEVELDURING START-UP OPERATIONS; 61/912,987 filed on Dec. 6, 2013 entitledMETHOD AND DEVICE FOR SEPARATING HYDROCARBONS AND CONTAMINANTS WITH ASURFACE TREATMENT MECHANISM.

BACKGROUND

Fields of Disclosure

The disclosure relates generally to the field of fluid separation. Morespecifically, the disclosure relates to the cryogenic separation ofcontaminants, such as acid gas, from a hydrocarbon.

Description of Related Art

This section is intended to introduce various aspects of the art, whichmay be associated with the present disclosure. This discussion isintended to provide a framework to facilitate a better understanding ofparticular aspects of the present disclosure. Accordingly, it should beunderstood that this section should be read in this light, and notnecessarily as admissions of prior art.

The production of natural gas hydrocarbons, such as methane and ethane,from a reservoir oftentimes carries with it the incidental production ofnon-hydrocarbon gases. Such gases include contaminants, such as at leastone of carbon dioxide (“CO₂”), hydrogen sulfide (“H₂S”), carbonylsulfide, carbon disulfide and various mercaptans. When a feed streambeing produced from a reservoir includes these contaminants mixed withhydrocarbons, the stream is oftentimes referred to as “sour gas.”

Many natural gas reservoirs have relatively low percentages ofhydrocarbons and relatively high percentages of contaminants.Contaminants may act as a diluent and lower the heat content ofhydrocarbons. Some contaminants, like sulfur-bearing compounds, arenoxious and may even be lethal. Additionally, in the presence of watersome contaminants can become quite corrosive.

It is desirable to remove contaminants from a stream containinghydrocarbons to produce sweet and concentrated hydrocarbons.Specifications for pipeline quality natural gas typically call for amaximum of 2-4% CO₂ and ¼ grain H₂S per 100 scf (4 ppmv) or 5 mg/Nm3H₂S. Specifications for lower temperature processes such as natural gasliquefaction plants or nitrogen rejection units typically require lessthan 50 ppm CO₂.

The separation of contaminants from hydrocarbons is difficult andconsequently significant work has been applied to the development ofhydrocarbon/contaminant separation methods. These methods can be placedinto three general classes: absorption by solvents (physical, chemicaland hybrids), adsorption by solids, and distillation.

Separation by distillation of some mixtures can be relatively simpleand, as such, is widely used in the natural gas industry. However,distillation of mixtures of natural gas hydrocarbons, primarily methane,and one of the most common contaminants in natural gas, carbon dioxide,can present significant difficulties. Conventional distillationprinciples and conventional distillation equipment are predicated on thepresence of only vapor and liquid phases throughout the distillationtower. The separation of CO₂ from methane by distillation involvestemperature and pressure conditions that result in solidification of CO₂if a pipeline or better quality hydrocarbon product is desired. Therequired temperatures are cold temperatures typically referred to ascryogenic temperatures.

Certain cryogenic distillations can overcome the above mentioneddifficulties. These cryogenic distillations provide the appropriatemechanism to handle the formation and subsequent melting of solidsduring the separation of solid-forming contaminants from hydrocarbons.The formation of solid contaminants in equilibrium with vapor-liquidmixtures of hydrocarbons and contaminants at particular conditions oftemperature and pressure takes place in a controlled freeze zonesection.

Sometimes solids can adhere to an internal (e.g., controlled freeze zonewall) of the controlled freeze zone section rather than falling to thebottom of the controlled freeze zone section.

The adherence is disadvantageous. The adherence, if uncontrolled, caninterfere with the proper operation of the controlled freeze zone andthe effective separation of methane from the contaminants.

A need exists for improved technology to destabilize and/or prevent anyadhesion of solids to surface(s) in the controlled freeze zone section.

SUMMARY

The present disclosure provides a device and method for separatingcontaminants from hydrocarbons and destabilizing and/or preventing theadhesion of solids to surface(s) in the controlled freeze section, amongother things.

The method for separating a feed stream in a distillation towercomprises introducing a feed stream into one of a stripper section and acontrolled freeze zone section of a distillation tower, the feed streamcomprising a hydrocarbon and a contaminant; separating the feed streamin the stripper section into an enriched contaminant bottom liquidstream, comprising the contaminant, and a freezing zone vapor stream,comprising the hydrocarbon, at a temperature and pressure at which nosolid forms; contacting the freezing zone vapor stream in the controlledfreeze zone section with a freezing zone liquid stream, comprising thehydrocarbon, at a temperature and pressure at which a solid, comprisingthe contaminant forms, and a vapor stream, further enriched in thehydrocarbon emerges; directly applying heat to the controlled freezezone wall of the controlled freeze zone section with a heating mechanismcoupled to at least one of a controlled freeze zone internal surface ofthe controlled freeze zone wall and a controlled freeze zone externalsurface of the controlled freeze zone wall; and at least one ofdestabilizing and preventing adhesion of the solid to the controlledfreeze zone wall with the heating mechanism.

The distillation tower that separates a contaminant in a feed streamfrom a hydrocarbon in the feed stream comprises a stripper sectionconstructed and arranged to separate a feed stream, comprising acontaminant and a hydrocarbon, into an enriched contaminant bottomliquid stream, comprising the contaminant, and a freezing zone vaporstream, comprising the hydrocarbon, at a temperature and pressure atwhich no solids form; a controlled freeze zone section comprising: amelt tray assembly at a bottom section of the controlled freeze zonesection that is constructed and arranged to melt a solid, comprising thecontaminant, formed in the controlled freeze zone section; a heatingmechanism coupled to at least one of a controlled freeze zone internalsurface of a controlled freeze zone wall of the controlled freeze zonesection and a controlled freeze zone external surface of the controlledfreeze zone wall that at least one of destabilizes and prevents adhesionof the solid to the controlled freeze zone wall, wherein the heatingmechanism is in an upper section of the controlled freeze zone sectionthat directly abuts and is separate from the bottom section.

A method for producing hydrocarbons may comprise extracting a feedstream comprising a hydrocarbon and a contaminant from a reservoir;introducing the feed stream into one of a stripper section and acontrolled freeze zone section of a distillation tower; separating thefeed stream in the stripper section into an enriched contaminant bottomliquid stream, comprising the contaminant, and a freezing zone vaporstream, comprising the hydrocarbon, at a temperature and pressure atwhich no solid forms; contacting the freezing zone vapor stream in thecontrolled freeze zone section with a freezing zone liquid stream,comprising the hydrocarbon, at a temperature and pressure at which thefreezing zone vapor stream forms a solid, comprising the contaminant,and a hydrocarbon-enriched vapor stream, comprising the hydrocarbon;directly applying heat to a controlled freeze zone wall of thecontrolled freeze zone section with a heating mechanism coupled to atleast one of a controlled freeze zone internal surface of the controlledfreeze zone wall and a controlled freeze zone external surface of thecontrolled freeze zone wall; at least one of destabilizing andpreventing adhesion of the solid to the controlled freeze zone wall withthe heating mechanism; removing the hydrocarbon-enriched vapor streamfrom the distillation tower; and producing the hydrocarbon-enrichedvapor stream extracted from the distillation tower.

The foregoing has broadly outlined the features of the presentdisclosure so that the detailed description that follows may be betterunderstood. Additional features will also be described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the disclosure willbecome apparent from the following description, appending claims and theaccompanying drawings, which are briefly described below.

FIG. 1 is a schematic diagram of a tower with sections within a singlevessel.

FIG. 2 is a schematic diagram of a tower with sections within multiplevessels.

FIG. 3 is a schematic diagram of a tower with sections within a singlevessel.

FIG. 4 is a schematic diagram of a tower with sections within multiplevessels.

FIG. 5 is a schematic, cross-sectional diagram of the controlled freezezone section of a distillation tower.

FIG. 6 is a schematic diagram of section 38 of FIG. 5 when the heatingmechanism comprises a heating coil.

FIG. 7 is a schematic diagram of section 38 of FIG. 5 when the heatingmechanism comprises an electrical conductor.

FIG. 8 is a flowchart of a method within the scope of the presentdisclosure.

It should be noted that the figures are merely examples and nolimitations on the scope of the present disclosure are intended thereby.Further, the figures are generally not drawn to scale, but are draftedfor purposes of convenience and clarity in illustrating various aspectsof the disclosure.

DETAILED DESCRIPTION

For the purpose of promoting an understanding of the principles of thedisclosure, reference will now be made to the features illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of thedisclosure is thereby intended. Any alterations and furthermodifications, and any further applications of the principles of thedisclosure as described herein are contemplated as would normally occurto one skilled in the art to which the disclosure relates. It will beapparent to those skilled in the relevant art that some features thatare not relevant to the present disclosure may not be shown in thedrawings for the sake of clarity.

As referenced in this application, the terms “stream,” “gas stream,”“vapor stream,” and “liquid stream” refer to different stages of a feedstream as the feed stream is processed in a distillation tower thatseparates methane, the primary hydrocarbon in natural gas, fromcontaminants. Although the phrases “gas stream,” “vapor stream,” and“liquid stream,” refer to situations where a gas, vapor, and liquid ismainly present in the stream, respectively, there may be other phasesalso present within the stream. For example, a gas may also be presentin a “liquid stream.” In some instances, the terms “gas stream” and“vapor stream” may be used interchangeably.

The disclosure relates to a system and method for separating a feedstream in a distillation tower. The system and method may destabilizesolids that may adhere and/or accumulate in the controlled freeze zonesection. The system and method may prevent solids that may adhere andaccumulate in the controlled freeze zone section from adhering and/oraccumulating. FIGS. 1-8 of the disclosure display various aspects of thesystem and method.

The system and method may separate a feed stream having methane andcontaminants. The system may comprise a distillation tower 104, 204(FIGS. 1-4). The distillation tower 104, 204 may separate thecontaminants from the methane.

The distillation tower 104, 204 may be separated into three functionalsections: a lower section 106, a middle controlled freeze zone section108 and an upper section 110. The distillation tower 104, 204 mayincorporate three functional sections when the upper section 110 isneeded and/or desired. The distillation tower 104, 204 may incorporateonly two functional sections when the upper section 110 is not neededand/or desired. When the distillation tower does not include an uppersection 110, a portion of vapor leaving the middle controlled freezezone section 108 may be extracted from the distillation tower 104, 204as line 21 for disposing the vapors off the middle controlled freezezone section while they are off specification with too high acontaminant content or for use as fuel or for other purposes, with theremaining vapor not extracted in line 14. Note that line 23 and line 14are directly connected in FIGS. 2 and 4 in this instance. Line 14 entersthe condenser 122 where a portion of the vapor may be condensed andreturned as a liquid spray stream via a spray assembly 129. Moreover,lines 18 and 20 in FIGS. 1 and 3 or line 18 in FIGS. 2 and 4 may beeliminated, elements 124 and 126 in FIGS. 1 and 3 may be one and thesame, and elements 150 and 128 in FIGS. 1 and 3 may be one and the same.The stream in line 14 in FIGS. 1 and 3, now taking the vapors leavingthe middle controlled freeze section 108, directs these vapors to thecondenser 122.

The lower section 106 may also be referred to as a stripper section. Themiddle controlled freeze zone section 108 may also be referred to as acontrolled freeze zone section. The upper section 110 may also bereferred to as a rectifier section.

The sections of the distillation tower 104 may be housed within a singlevessel (FIGS. 1 and 3). For example, the lower section 106, the middlecontrolled freeze zone section 108, and the upper section 110 may behoused within a single vessel 164.

The sections of the distillation tower 204 may be housed within aplurality of vessels to form a split-tower configuration (FIGS. 2 and4). Each of the vessels may be separate from the other vessels. Pipingand/or another suitable mechanism may connect one vessel to anothervessel. In this instance, the lower section 106, middle controlledfreeze zone section 108 and upper section 110 may be housed within twoor more vessels. For example, as shown in FIGS. 2 and 4, the uppersection 110 may be housed within a single vessel 254 and the lower andmiddle controlled freeze zone sections 106, 108 may be housed within asingle vessel 264. When this is the case, a liquid stream exiting theupper section 110, may exit through a liquid outlet bottom 260. Theliquid outlet bottom 260 is at the bottom of the upper section 110.Although not shown, each of the sections may be housed within its ownseparate vessel, or one or more section may be housed within separatevessels, or the upper and middle controlled freeze zone sections may behoused within a single vessel and the lower section may be housed withina single vessel, etc. When sections of the distillation tower are housedwithin vessels, the vessels may be side-by-side along a horizontal lineand/or above each other along a vertical line.

The split-tower configuration may be beneficial in situations where theheight of the distillation tower, motion considerations, and/ortransportation issues, such as for remote locations, need to beconsidered. This split-tower configuration allows for the independentoperation of one or more sections. For example, when the upper sectionis housed within a single vessel and the lower and middle controlledfreeze zone sections are housed within a single vessel, independentgeneration of reflux liquids using a substantially contaminant-free,largely hydrocarbon stream from a packed gas pipeline or an adjacenthydrocarbon line, may occur in the upper section. And the reflux may beused to cool the upper section, establish an appropriate temperatureprofile in the upper section, and/or build up liquid inventory at thebottom of the upper section to serve as an initial source of sprayliquids for the middle controlled freeze zone section. Moreover, themiddle controlled freeze zone and lower sections may be independentlyprepared by chilling the feed stream, feeding it to the optimal locationbe that in the lower section or in the middle controlled freeze zonesection, generating liquids for the lower and the middle controlledfreeze zone sections, and disposing the vapors off the middle controlledfreeze zone section while they are off specification with too high acontaminant content. Also, liquid from the upper section may beintermittently or continuously sprayed, building up liquid level in thebottom of the middle controlled freeze zone section and bringing thecontaminant content in the middle controlled freeze zone section downand near steady state level so that the two vessels may be connected tosend the vapor stream from the middle controlled freeze zone section tothe upper section, continuously spraying liquid from the bottom of theupper section into the middle controlled freeze zone section andstabilizing operations into steady state conditions. The split towerconfiguration may utilize a sump of the upper section as a liquidreceiver for the pump 128, therefore obviating the need for a liquidreceiver 126 in FIGS. 1 and 3.

The system may also include a heat exchanger 100 (FIGS. 1-4). The feedstream 10 may enter the heat exchanger 100 before entering thedistillation tower 104, 204. The feed stream 10 may be cooled within theheat exchanger 100. The heat exchanger 100 helps drop the temperature ofthe feed stream 10 to a level suitable for introduction into thedistillation tower 104, 204.

The system may include an expander device 102 (FIGS. 1-4). The feedstream 10 may enter the expander device 102 before entering thedistillation tower 104, 204. The feed stream 10 may be expanded in theexpander device 102 after exiting the heat exchanger 100. The expanderdevice 102 helps drop the temperature of the feed stream 10 to a levelsuitable for introduction into the distillation tower 104, 204. Theexpander device 102 may be any suitable device, such as a valve. If theexpander device 102 is a valve, the valve may be any suitable valve thatmay aid in cooling the feed stream 10 before it enters the distillationtower 104, 204. For example, the expander device 102 may comprise aJoule-Thompson (J-T) valve.

The system may include a feed separator 103 (FIGS. 3-4). The feed streammay enter the feed separator before entering the distillation tower 104,204. The feed separator may separate a feed stream having a mixed liquidand vapor stream into a liquid stream and a vapor stream. Lines 12 mayextend from the feed separator to the distillation tower 104, 204. Oneof the lines 12 may receive the vapor stream from the feed separator.Another one of the lines 12 may receive the liquid stream from the feedseparator. Each of the lines 12 may extend to the same and/or differentsections (i.e. middle controlled freeze zone, and lower sections) of thedistillation tower 104, 204. The expander device 102 may or may not bedownstream of the feed separator 103. The expander device 102 maycomprise a plurality of expander devices 102 such that each line 12 hasan expander device 102.

The system may include a dehydration unit 261 (FIGS. 1-4). The feedstream 10 may enter the dehydration unit 261 before entering thedistillation tower 104, 204. The feed stream 10 enters the dehydrationunit 261 before entering the heat exchanger 100 and/or the expanderdevice 102. The dehydration unit 261 removes water from the feed stream10 to prevent water from later presenting a problem in the heatexchanger 100, expander device 102, feed separator 103, or distillationtower 104, 204. The water can present a problem by forming a separatewater phase (i.e., ice and/or hydrate) that plugs lines, equipment ornegatively affects the distillation process. The dehydration unit 261dehydrates the feed stream to a dew point sufficiently low to ensure aseparate water phase does not form at any point downstream during therest of the process. The dehydration unit may be any suitabledehydration mechanism, such as a molecular sieve or a glycol dehydrationunit.

The system may include a filtering unit (not shown). The feed stream 10may enter the filtering unit before entering the distillation tower 104,204. The filtering unit may remove undesirable contaminants from thefeed stream before the feed stream enters the distillation tower 104,204. Depending on what contaminants are to be removed, the filteringunit may be before or after the dehydration unit 261 and/or before orafter the heat exchanger 100.

The system may include a line 12 (FIGS. 1-4). The line may also bereferred to as an inlet channel 12. The feed stream 10 may be introducedinto the distillation tower 104, 204 through the line 12. The line 12may extend to the lower section 106 or the middle controlled freeze zonesection 108 of the distillation tower 104, 204. For example, the line 12may extend to the lower section 106 such that the feed stream 10 mayenter the lower section 106 of the distillation tower 104, 204 (FIGS.1-4). The line 12 may directly or indirectly extend to the lower section106 or the middle controlled freeze zone section 108. The line 12 mayextend to an outer surface of the distillation tower 104, 204 beforeentering the distillation tower.

The lower section 106 is constructed and arranged to separate the feedstream 10 into an enriched contaminant bottom liquid stream (i.e.,liquid stream) and a freezing zone vapor stream (i.e., vapor stream).The lower section 106 separates the feed stream at a temperature andpressure at which no solids form. The liquid stream may comprise agreater quantity of contaminants than of methane. The vapor stream maycomprise a greater quantity of methane than of contaminants. In anycase, the vapor stream is lighter than the liquid stream. As a result,the vapor stream rises from the lower section 106 and the liquid streamfalls to the bottom of the lower section 106.

The lower section 106 may include and/or connect to equipment thatseparates the feed stream. The equipment may comprise any suitableequipment for separating methane from contaminants, such as one or morepacked sections 181, or one or more distillation trays withperforations, downcomers, and weirs (FIGS. 1-4).

The equipment may include components that apply heat to the stream toform the vapor stream and the liquid stream. For example, the equipmentmay comprise a first reboiler 112 that applies heat to the stream. Thefirst reboiler 112 may be located outside of the distillation tower 104,204. The equipment may also comprise a second reboiler 172 that appliesheat to the stream. The second reboiler 172 may be located outside ofthe distillation tower 104, 204. Line 117 may lead from the distillationtower to the second reboiler 172. Line 17 may lead from the secondreboiler 172 to the distillation tower. Additional reboilers, set upsimilarly to the second reboiler described above, may also be used.

The first reboiler 112 may apply heat to the liquid stream that exitsthe lower section 106 through a liquid outlet 160 of the lower section106. The liquid stream may travel from the liquid outlet 160 throughline 28 to reach the first reboiler 112 (FIGS. 1-4). The amount of heatapplied to the liquid stream by the first reboiler 112 can be increasedto separate more methane from contaminants. The more heat applied by thefirst reboiler 112 to the stream, the more methane separated from theliquid contaminants, though more contaminants will also be vaporized.

The first reboiler 112 may also apply heat to the stream within thedistillation tower 104, 204. Specifically, the heat applied by the firstreboiler 112 warms up the lower section 106. This heat travels up thelower section 106 and supplies heat to warm solids entering a melt trayassembly 139 (FIGS. 1-4) of the middle controlled freeze zone section108 so that the solids form a liquid and/or slurry mix.

The second reboiler 172 applies heat to the stream within the lowersection 106. This heat is applied closer to the middle controlled freezezone section 108 than the heat applied by the first reboiler 112. As aresult, the heat applied by the second reboiler 172 reaches the middlecontrolled freeze zone section 108 faster than the heat applied by thefirst reboiler 112. The second reboiler 172 also helps with energyintegration.

The equipment may include a chimney assembly 135 (FIGS. 1-4). Whilefalling to the bottom of the lower section 106, the liquid stream mayencounter one or more of the chimney assemblies 135.

Each chimney assembly 135 includes a chimney tray 131 that collects theliquid stream within the lower section 106. The liquid stream thatcollects on the chimney tray 131 may be fed to the second reboiler 172.After the liquid stream is heated in the second reboiler 172, the streammay return to the middle controlled freeze zone section 106 to supplyheat to the middle controlled freeze zone section 106 and/or the melttray assembly 139. Unvaporized stream exiting the second reboiler 172may be fed back to the distillation tower 104, 204 below the chimneytray 131. Vapor stream exiting the second reboiler 172 may be routedunder or above the chimney tray 131 when the vapor stream enters thedistillation tower 104, 204.

The chimney tray 131 may include one or more chimneys 137. The chimney137 serves as a channel that the vapor stream in the lower section 106traverses. The vapor stream travels through an opening in the chimneytray 131 at the bottom of the chimney 137 to the top of the chimney 137.The opening is closer to the bottom of the lower section 106 than it isto the bottom of the middle controlled freeze zone section 108. The topis closer to the bottom of the middle controlled freeze zone section 108than it is to the bottom of the lower section 106.

Each chimney 137 has attached to it a chimney cap 133. The chimney cap133 covers a chimney top opening 138 of the chimney 137. The chimney cap133 prevents the liquid stream from entering the chimney 137. The vaporstream exits the chimney assembly 135 via the chimney top opening 138.

After falling to the bottom of the lower section 106, the liquid streamexits the distillation tower 104, 204 through the liquid outlet 160. Theliquid outlet 160 is within the lower section 106 (FIGS. 1-4). Theliquid outlet 160 may be located at the bottom of the lower section 106.

After exiting through the liquid outlet 160, the feed stream may travelvia line 28 to the first reboiler 112. The feed stream may be heated bythe first reboiler 112 and vapor may then re-enter the lower section 106through line 30. Unvaporized liquid may continue out of the distillationprocess via line 24.

The system may include an expander device 114 (FIGS. 1-4). Afterentering line 24, the heated liquid stream may be expanded in theexpander device 114. The expander device 114 may be any suitable device,such as a valve. The valve 114 may be any suitable valve, such as a J-Tvalve.

The system may include a heat exchanger 116 (FIGS. 1-4). The liquidstream heated by the first reboiler 112 may be cooled or heated by theheat exchanger 116. The heat exchanger 116 may be a direct heatexchanger or an indirect heat exchanger. The heat exchanger 116 maycomprise any suitable heat exchanger.

The vapor stream in the lower section 106 rises from the lower section106 to the middle controlled freeze zone section 108. The middlecontrolled freeze zone section 108 is constructed and arranged toseparate the feed stream 10 introduced into the middle controlled freezezone section, or into the top of lower section 106, into a solid and avapor stream. The solid may be comprised more of contaminants than ofmethane. The vapor stream (i.e., methane-enriched vapor stream) maycomprise more methane than contaminants.

The middle controlled freeze zone section 108 includes a lower section40 and an upper section 39 (FIG. 5). The lower section 40 is below theupper section 39. The lower section 40 directly abuts the upper section39. The lower section 40 is primarily but not exclusively a heatingsection of the middle controlled freeze zone section 108. The uppersection 39 is primarily but not exclusively a cooling section of themiddle controlled freeze zone section 108. The temperature and pressureof the upper section 39 are chosen so that the solid can form in themiddle controlled freeze zone section 108.

The middle controlled freeze zone section 108 may comprise a melt trayassembly 139 that is maintained in the middle controlled freeze zonesection 108 (FIGS. 1-4). The melt tray assembly 139 is within the lowersection 40 of the middle controlled freeze zone section 108. The melttray assembly 139 is not within the upper section 39 of the middlecontrolled freeze zone section 108.

The melt tray assembly 139 is constructed and arranged to melt a solidformed in the middle controlled freeze zone section 108. When the warmvapor stream rises from the lower section 106 to the middle controlledfreeze zone section 108, the vapor stream immediately encounters themelt tray assembly 139 and supplies heat to melt the solids. The melttray assembly 139 may comprise at least one of a melt tray 118, a bubblecap 132, a liquid 130 and heat mechanism(s) 134.

The melt tray 118 may collect a liquid and/or slurry mix. The melt tray118 divides at least a portion of the middle controlled freeze zonesection 108 from the lower section 106. The melt tray 118 is at thebottom 45 of the middle controlled freeze zone section 108.

One or more bubble caps 132 may act as a channel for the vapor streamrising from the lower section 106 to the middle controlled freeze zonesection 108. The bubble cap 132 may provide a path for the vapor streamup the riser 140 and then down and around the riser 140 to the melt tray118. The riser 140 is covered by a cap 141. The cap 141 prevents theliquid 130 from travelling into the riser and it also helps preventsolids from travelling into the riser 140. The vapor stream's traversalthrough the bubble cap 132 allows the vapor stream to transfer heat tothe liquid 130 within the melt tray assembly 139.

One or more heat mechanisms 134 may further heat up the liquid 130 tofacilitate melting of the solids into a liquid and/or slurry mix. Theheat mechanism(s) 134 may be located anywhere within the melt trayassembly 139. For example, as shown in FIGS. 1-4, a heat mechanism 134may be located around bubble caps 132. The heat mechanism 134 may be anysuitable mechanism, such as a heat coil. The heat source of the heatmechanism 134 may be any suitable heat source.

The liquid 130 in the melt tray assembly 139 is heated by the vaporstream. The liquid 130 may also be heated by the one or more heatmechanisms 134. The liquid 130 helps melt the solids formed in themiddle controlled freeze zone section 108 into a liquid and/or slurrymix. Specifically, the heat transferred by the vapor stream heats up theliquid, thereby enabling the heat to melt the solids. The liquid 130 isat a level sufficient to melt the solids.

While in the liquid 130, hydrocarbons may be separated from thecontaminants. The hydrocarbons separated from the contaminants may formpart of the vapor stream (i.e., the hydrocarbon-enriched vapor stream),and may rise from the lower section 40 to the upper section 39 of themiddle controlled freeze zone section 108.

The middle controlled freeze zone section 108 may include a heatingmechanism 36, 136. The heating mechanism 36, 136 may be coupled to atleast one of a controlled freeze zone internal surface 31 (FIG. 5) of acontrolled freeze zone wall 46 (FIG. 5) and a controlled freeze zoneexternal surface 47 (FIGS. 5-7) of the controlled freeze zone wall 46.

The controlled freeze zone internal surface 31 is the inside surface ofthe middle controlled freeze zone section 108 (FIG. 5). The controlledfreeze zone internal surface 31 may not be the innermost inside surfaceof the middle controlled freeze zone section 108 when the heatingmechanism is coupled to the controlled freeze zone internal surface 31.The heating mechanism may be the innermost inside surface of the middlecontrolled freeze zone section 108.

The controlled freeze zone external surface 47 is the outside surface ofthe middle controlled freeze zone section 108 (FIG. 5). The controlledfreeze zone external surface 47 may not be the outermost surface of themiddle controlled freeze zone section 108.

Insulation 34 and its cladding 35 may be on top of the controlled freezezone external surface 47 (FIG. 5). The insulation 34 and its cladding 35may be the outermost surface of the middle controlled freeze zonesection 108. The insulation 34 may be on top of the controlled freezezone external surface 47 such that the controlled freeze zone externalsurface 47 may be on an outer surface of the middle controlled freezezone section 108.

The heating mechanism 36, 136 may be controlled in a manner to provideoptimal amount of heat to destabilize and/or prevent adhesion of solidsin the middle controlled freeze zone section 108. The heating mechanism36, 136 may be controlled in a manner to prevent any adverse effectsfrom excessive heat input into the middle controlled freeze zone section108. In essence, the coupling is controlled such that heat emitted bythe heating mechanism 36, 136 is localized to the controlled freeze zonewall 46 where solids adhere.

To provide an optimal amount of heat, the heating mechanism 36, 136 maybe controlled by a temperature controller or by an electrical powercontroller. The temperature controller controls the temperature of theheating mechanism 36, 136. The electrical power controller controls theelectrical power of the heating mechanism 36, 136.

The heating mechanism 36, 136 may be above and/or below the uppermostportion of the melt tray assembly 139 of the middle controlled freezezone section 108. The heating mechanism 36, 136 may be in the uppermostsection 39 of the middle controlled freeze zone section 108.

The heating mechanism 36, 136 may comprise one or more heatingmechanisms 36, 136. For example, as shown in FIGS. 5-7, the heatingmechanism 36, 136 may comprise three heating mechanisms. Each of theheating mechanisms 36, 136 may be directly adjacent to another of theheating mechanisms. One or more of the heating mechanisms 36, 136 may bewithin a heating zone of the middle controlled freeze zone section 108.Each of the heating mechanisms 36, 136 within the heating zone isresponsible for heating the portion of the controlled freeze zone wall46 within the heating zone. There may be a plurality of heating zones.

When the heating mechanism 36, 136 comprises multiple heatingmechanisms, one or more of the heating mechanisms may or may not beconnected together. When heating mechanisms are connected, the heatingmechanisms may be operated together. When heating mechanisms are notconnected, the heating mechanisms may be operated independently. Theindependent operation of heating mechanisms may allow for optimalheating control of one or more heating zones of the middle controlledfreeze zone section 108. The independent operation of heating mechanismsmay allow less total heating of the middle controlled freeze zonesection 108, thereby improving the efficiency of the distillation tower104, 204. When the heating mechanisms are connected, the heatingmechanisms may be operated dependently. The dependent operation of theheating mechanisms may allow for the heating mechanisms to be operatedmore simplistically than independent operation of the heating mechanism.

The amount and/or size of heating mechanisms 36, 136 in the middlecontrolled freeze zone section 108 may depend on a variety of factors.The factors may include the size of the distillation tower 104, 204, thethickness of the controlled freeze zone wall 46, the temperature of theliquid spray stream being sprayed from the spray assembly 129, the flowrate of the feed stream 10, and/or the temperature outside of thedistillation tower 104, 204. The more feed stream 10 that enters thedistillation tower 104, 204, the more liquid spray stream sprayed. Thethicker the controlled freeze zone wall 46 and/or lower the temperatureoutside of the distillation tower 104, 204, the more heat the heatingmechanism 36, 136 may need to produce.

The heating mechanism 36, 136 destabilizes and/or prevents adhesion ofthe solids to the controlled freeze zone wall 46. When fully heated, thetemperature of the heating mechanism 36, 136 is above the solidificationtemperature of the solid. Consequently, the ability of the solid toaccumulate and/or adhere to the controlled freeze zone wall 46 isreduced because the adhesion of the solids to the controlled freeze zonewall 46 is prevented and/or adhered solids are destabilized by theheating mechanism 36, 136. To the extent that any solid has adhered tothe controlled freeze zone wall 46, such as before the heating mechanism36, 136 is turned on or has heated up to be a temperature above thesolidification temperature of the solid, or because of an operationalupset, the heating mechanism 36, 136 causes the solid to detach from thecontrolled freeze zone wall 46 after the heating mechanism 36, 136 is ata temperature above the solidification temperature of the solid.

The heating mechanism 36, 136 may completely extend around at least oneof an internal circumference 49 of the controlled freeze zone internalsurface 31 and an external circumference 51 of the controlled freezezone external surface 47. Alternatively, the heating mechanism 36, 136may extend around a portion of at least one of the internalcircumference 49 and the external circumference 51. The amount of theinternal or external circumference that the heating mechanism 36, 136extends around depends on the amount of the controlled freeze zone wall46 heated by the heating mechanism 36, 136.

The heating mechanism 36, 136 may be any suitable heating mechanism 36,136. For example, the heating mechanism 36, 136 may be one of a coil 42(FIG. 6) and an electrical conductor 43 (FIG. 7). When the heatingmechanism 36, 136 is coupled to the controlled freeze zone internalsurface 31, the heating mechanism 36, 136 may be any source of heat thatcan be safely deployed inside a distillation tower without, for example,being a potential source of combustion.

When the heating mechanism 36, 136 is a coil, the coil 42 may receive afluid at a temperature above the solidification temperature of thesolid. The fluid within the coil 42 transfers heat to at least one ofthe controlled freeze zone wall 46, the inside of the upper section 39of the middle controlled freeze zone section 108, and the liquid on themelt tray 118. The transferred heat destabilizes and/or prevents theadhesion of the solid to the controlled freeze zone wall 46. The fluidwithin the coil 42 directly transfers heat to the controlled freeze zonewall 46 when the coil 42 is coupled to the controlled freeze zoneexternal surface 47 or the controlled freeze zone internal surface 31.When the heating mechanism 36, 136 is coupled to the controlled freezezone internal surface 31, the heating mechanism 36, 136 is a coil 42 toavoid the potential of a fire occurring inside the distillation tower104, 204. The fluid within the coil may be any suitable fluid. Forexample, the fluid may be any fluid whose inlet temperature and/or flowrate can be controlled, and whose freezing point is substantially lowerthan that of the freezing CO₂. Examples of fluid include, but are notlimited to, propane, methanol, and/or other commercially-availablelow-melting temperature heat transfer fluids.

When the heating mechanism 36, 136 is an electrical conductor 43, theelectrical conductor operates at a temperature above the solidificationtemperature of the solid. The electrical conductor 43 may be anysuitable electrical conductor 43. For example, the electrical conductor43 may comprise aluminum solid alloy or copper. The heating mechanism36, 136 may be an electrical conductor 43 when the heating mechanism 36,136 is coupled to the controlled freeze zone external surface 47 and notthe controlled freeze zone internal surface 31 to avoid the potential ofa fire occurring inside the distillation tower.

A certain amount of heat may be applied by the heating mechanism 36, 136to ensure destabilization of solids and/or to prevent adhesion of solidswithin the middle controlled freeze zone section 108. The certain amountof heat is enough heat to bring an internal surface of the middlecontrolled freeze zone section 108 to a temperature slightly above thefreezing point of CO₂. The certain amount of heat is not excessive so asto not to impact negatively the normal operation of the middlecontrolled freeze zone section 108.

Previous technology did not supply heat by a heating mechanism 36, 136within a middle controlled freeze zone section 108 because it was notexpected that solids would adhere to the middle controlled freeze zonesection. Instead it was expected that solids would fall to the melt trayassembly 139 without adhering to the middle controlled freeze zonesection. It was also not expected that the elements within the middlecontrolled freeze zone section would interfere with the pathway of thesolids such that the solids would adhere to the middle controlled freezezone section instead of falling to the melt tray assembly 139.

A temperature of the heating mechanism 36, 136 and/or the controlledfreeze zone wall 46 may be detected with a temperature sensor 142, 243(FIGS. 6-7). When the middle controlled freeze zone section 108 includesmultiple heating mechanisms 36, 136, the temperature of one or more ofthe heating mechanism 36, 136 may be detected with the temperaturesensors.

The middle controlled freeze zone section 108 may include thetemperature sensor 142, 243. The temperature sensor 142, 243 may be onany surface of the middle controlled freeze zone section 108. Forexample, the temperature sensor may be at least one of coupled to thecontrolled freeze zone internal surface 31 (FIG. 5), the controlledfreeze zone external surface 47 and the insulation 34. Surfaces of themiddle controlled freeze zone section 108 include the controlled freezezone internal surface 31, the controlled freeze zone external surface47, the insulation 34, surfaces of the spray assembly 129, surfaces ofthe melt tray assembly 139, etc. The temperature sensor 142, 243 may bewithin at least one of the lower section 40 and the upper section 39 ofthe middle controlled freeze zone section 108. Temperature sensors maybe spaced at intervals throughout the middle controlled freeze zonesection 108.

The temperature sensor 142, 243 detects temperature at and/or around thearea surrounding the temperature sensor 142, 243. A baseline temperaturefor each temperature sensor 142, 243 is determined while the middlecontrolled freeze zone section 108 is properly functioning. Atemperature deviation outside of an expected temperature range of thetemperature detected by the temperature sensor 142, 243 (i.e., thedetected temperature) from the baseline temperature may indicate thatthe middle controlled freeze zone section 108 is not properlyfunctioning. The temperature deviation may be about 2 to 10 degrees C.or 2 to 10 degrees C.

The middle controlled freeze zone section 108 may be deemed to be notproperly functioning if one or more of a variety of circumstances occur.The variety of circumstances may include if solids build-up on thecontrolled freeze zone wall 46, if the middle controlled freeze zonesection 108 is too warm to form solids, if the middle controlled freezezone section 108 is too cold to melt the solids in the melt trayassembly 139, etc. For example, if the temperature sensor 142, 243 iscoupled to the controlled freeze zone external surface 47 within theupper section 39 of the middle controlled freeze zone section 108 thenthe temperature sensor 142, 243 is expected to detect a fairly coldtemperature that is close to the actual temperature of the liquid spraystream within the middle controlled freeze zone section 108. If thetemperature sensor 142, 243 detects a rise in temperature from thatexpected of the actual temperature of the liquid spray stream, then therise in temperature may indicate that solids have built-up on thecontrolled freeze zone wall 46. The solid acts as an insulator so solidbuild-up on the controlled freeze zone wall 46 is determined when thereis an unexpected rise in temperature read by the temperature sensor 142,243.

As it relates to the heating mechanism, the detected temperature helpsdetermine whether the heating mechanism 36, 136 is working in a mannerto destabilize and/or prevent adhesion of solid on the controlled freezezone wall 46. If the temperature detected by the temperature sensor 142,243 falls outside of the expected temperature range, the temperaturesensor 142, 243 may indicate that the heating mechanism 36, 136 is notworking in a manner to destabilize and/or prevent adhesion of solid onthe controlled freeze zone wall 46. In this instance, the heatingmechanism 36, 136 may be manipulated to apply more heat to thecontrolled freeze zone wall 46. In addition or alternatively, measuresmay be taken to destabilize and/or prevent adhesion of the solid to thecontrolled freeze zone wall 46. The measures may include at least one of(a) applying a treatment mechanism and (b) using a modified sprayassembly, such as those described in the applications entitled “Methodand Device for Separating Hydrocarbons and Contaminants with a SurfaceTreatment Mechanism” (U.S. Ser. No. 61/912,987) and “Method and Devicefor Separating Hydrocarbons and Contaminants with a Spray Assembly,”(U.S. Ser. No. 61/912,957) respectively, each by Jaime Valencia, et al.and filed on the same day as the instant application.

The temperature sensor 142, 243 may be any suitable temperature sensor.For example, the temperature sensor may comprise a thermocouple,platinum resistance thermometer, RTD and/or thermistor.

The temperature sensor 142, 243 may comprise a plurality of temperaturesensors 142, 243. Each of the plurality of temperature sensors 142, 243may be coupled to the same or different surface of the middle controlledfreeze zone section 108. One or more of the temperature sensors 142, 243may comprise an array of temperature sensors. One or more of thetemperature sensors may be coupled to a surface of the middle controlledfreeze zone section 108 at the same or different elevation of the middlecontrolled freeze zone section 108. While the temperature sensor 142,243 is generally referred to as part of the middle controlled freezezone section 108, a temperature sensor 142, 243 could be included in oneor more of the lower section 106 and the upper section 110.

When the middle controlled freeze zone section 108 includes a heatingmechanism 36, 136, the controlled freeze zone internal surface 31 maynot have a treatment mechanism, such as the treatment mechanismdescribed in the application entitled “Method and Device for SeparatingHydrocarbons and Contaminants with a Surface Treatment Mechanism” (U.S.Ser. No. 61/912,987) by Jaime Valencia, et al and filed on the same dayas the instant application. The middle controlled freeze zone section108 including the heating mechanism 36, 136 may not use the treatmentmechanism because the heating mechanism 36, 136 may adequatelydestabilize and/or prevent the adhesion of solids to the controlledfreeze zone wall 46 without also being treated by the treatmentmechanism. Alternatively, the middle controlled freeze zone section 108including the heating mechanism 36, 136 may have the controlled freezezone internal surface 31 treated with the treatment mechanism. Havingthe heating mechanism 36, 136 and controlled freeze zone internalsurface 31 treated with the treatment mechanism may allow for a reducedenergy input.

The middle controlled freeze zone section 108 may also comprise a sprayassembly 129. The spray assembly 129 cools the vapor stream that risesfrom the lower section 40. The spray assembly 129 sprays liquid, whichis cooler than the vapor stream, on the vapor stream to cool the vaporstream. The spray assembly 129 is within the upper section 39. The sprayassembly 129 is not within the lower section 40. The spray assembly 129is above the melt tray assembly 139. In other words, the melt trayassembly 139 is below the spray assembly 129.

The spray assembly 129 includes one or more spray nozzles 120 (FIGS.1-4). Each spray nozzle 120 sprays liquid on the vapor stream. The sprayassembly 129 may also include a spray pump 128 (FIGS. 1-4) that pumpsthe liquid. Instead of a spray pump 128, gravity may induce flow in theliquid.

The liquid sprayed by the spray assembly 129 contacts the vapor streamat a temperature and pressure at which solids form. Solids, containingmainly contaminants, form when the sprayed liquid contacts the vaporstream, 502 (FIG. 8). The solids fall toward the melt tray assembly 139.

The temperature in the middle controlled freeze zone section 108 coolsdown as the vapor stream travels from the bottom of the middlecontrolled freeze zone section 108 to the top of the middle controlledfreeze zone section 108. The methane in the vapor stream rises from themiddle controlled freeze zone section 108 to the upper section 110. Somecontaminants may remain in the methane and also rise. The contaminantsin the vapor stream tend to condense or solidify with the coldertemperatures and fall to the bottom of the middle controlled freeze zonesection 108.

The solids form the liquid and/or slurry mix when in the liquid 130.Some of the liquid and/or slurry mix flows from the middle controlledfreeze zone section 108 to the lower section 106. This liquid and/orslurry mix flows from the bottom of the middle controlled freeze zonesection 108 to the top of the lower section 106 via a line 22 (FIGS.1-4). The line 22 may be an exterior line. The line 22 may extend fromthe distillation tower 104, 204. The line 22 may extend from the middlecontrolled freeze zone section 108. The line may extend to the lowersection 106. The line 22 may extend from an outer surface of thedistillation tower 104, 204.

The vapor stream that rises in the middle controlled freeze zone section108 and does not form solids or otherwise fall to the bottom of themiddle controlled freeze zone section 108, rises to the upper section110. The upper section 110 operates at a temperature and pressure andcontaminant concentration at which no solid forms. The upper section 110is constructed and arranged to cool the vapor stream to separate themethane from the contaminants. Reflux in the upper section 110 cools thevapor stream. The reflux is introduced into the upper section 110 vialine 18. Line 18 may extend to the upper section 110. Line 18 may extendfrom an outer surface of the distillation tower 104, 204.

After contacting the reflux in the upper section 110, the feed streamforms a vapor stream and a liquid stream. The vapor stream mainlycomprises methane. The liquid stream comprises relatively morecontaminants. The vapor stream rises in the upper section 110 and theliquid falls to a bottom of the upper section 110.

To facilitate separation of the methane from the contaminants when thestream contacts the reflux, the upper section 110 may include one ormore mass transfer devices 176. Each mass transfer device 176 helpsseparate the methane from the contaminants. Each mass transfer device176 may comprise any suitable separation device, such as a tray withperforations, or a section of random or structured packing to facilitatecontact of the vapor and liquid phases.

After rising, the vapor stream may exit the distillation tower 104, 204through line 14. The line 14 may emanate from an upper part of the uppersection 110. The line 14 may extend from an outer surface of the uppersection 110.

From line 14, the vapor stream may enter a condenser 122. The condenser122 cools the vapor stream to form a cooled stream. The condenser 122 atleast partially condenses the stream.

After exiting the condenser 122, the cooled stream may enter a separator124. The separator 124 separates the vapor stream into liquid and vaporstreams. The separator may be any suitable separator that can separate astream into liquid and vapor streams, such as a reflux drum.

Once separated, the vapor stream may exit the separator 124 as salesproduct. The sales product may travel through line 16 for subsequentsale to a pipeline and/or condensation to be liquefied natural gas.

Once separated, the liquid stream may return to the upper section 110through line 18 as the reflux. The reflux may travel to the uppersection 110 via any suitable mechanism, such as a reflux pump 150 (FIGS.1 and 3) or gravity (FIGS. 2 and 4).

The liquid stream (i.e., freezing zone liquid stream) that falls to thebottom of the upper section 110 collects at the bottom of the uppersection 110. The liquid may collect on tray 183 (FIGS. 1 and 3) or atthe bottommost portion of the upper section 110 (FIGS. 2 and 4). Thecollected liquid may exit the distillation tower 104, 204 through line20 (FIGS. 1 and 3) or outlet 260 (FIGS. 2 and 4). The line 20 mayemanate from the upper section 110. The line 20 may emanate from abottom end of the upper section 110. The line 20 may extend from anouter surface of the upper section 110.

The line 20 and/or outlet 260 connect to a line 41. The line 41 leads tothe spray assembly 129 in the middle controlled freeze zone section 108.The line 41 emanates from the holding vessel 126. The line 41 may extendto an outer surface of the middle controlled freeze zone section 110.

The line 20 and/or outlet 260 may directly or indirectly (FIGS. 1-4)connect to the line 41. When the line 20 and/or outlet 260 directlyconnect to the line 41, the liquid spray may be sent to the spraynozzle(s) 120 via any suitable mechanism, such as the spray pump 128 orgravity. When the line 20 and/or outlet 260 indirectly connect to theline 41, the lines 20, 41 and/or outlet 260 and line 41 may directlyconnect to a holding vessel 126 (FIGS. 1 and 3). The holding vessel 126may house at least some of the liquid spray before it is sprayed by thenozzle(s). The liquid spray may be sent from the holding vessel 126 tothe spray nozzle(s) 120 via any suitable mechanism, such as the spraypump 128 (FIGS. 1-4) or gravity. The holding vessel 126 may be neededwhen there is not a sufficient amount of liquid stream at the bottom ofthe upper section 110 to feed the spray nozzles 120.

Persons skilled in the technical field will readily recognize that inpractical applications, the use of one or more heating mechanisms todestabilize and/or prevent the adhesion of solids to a surface may beused in other apparatuses and/or systems beside distillation towers. Forexample, one or more heating mechanisms may be used in a physicalremoval process.

As shown in FIG. 8, a method for separating a feed stream 10 in thedistillation tower 104, 204 and/or producing hydrocarbons may includeintroducing 500 the feed stream 10 into a section 106, 108 of thedistillation tower 104, 204. As previously discussed in the instantapplication, the feed stream 10 is introduced into one of the sections106, 108 via line 12. The method may also include separating 501 thefeed stream 10 in the lower section 106 into the enriched contaminantbottom liquid stream and the freezing zone vapor stream at a temperatureand pressure at which no solid forms. The lower section 106 operates aspreviously discussed in the instant application. Additionally, themethod may include contacting 502 the freezing zone vapor stream in themiddle controlled freeze zone section 108 with the freezing zone liquidstream at a temperature and pressure at which the freezing zone vaporstream forms the solid and the hydrocarbon-enriched vapor stream. Themiddle controlled freeze zone section 108 operates as previouslydiscussed in the instant application. Moreover, the method may includedirectly applying heat 503 to the controlled freeze zone wall 46 anddestabilizing and/or preventing 504 adhesion of the solid to thecontrolled freeze zone wall 46 with the heating mechanism 36, 136. Theheating mechanism 36, 136 operates as previously discussed in theinstant application.

The method may also include detecting a temperature of at least one ofthe heating mechanism 36, 136 and the controlled freeze zone wall 46.The temperature may be detected using the temperature sensor 142, 243previously described. Information detected by the temperature sensor142, 243 may be used as previously described.

The method may include maintaining an upper section 110. The uppersection 110 operates as previously discussed in the instant application.The method may also include separating the feed stream in the uppersection 110 as previously discussed in the instant application.

The method may include stabilizing the distillation tower 104, 204 via asuitable operational action if large amounts of solid are destabilizedand fall into the melt tray assembly 139. One example of a suitableoperational action includes, but is not limited to, controlling theliquid level in the melt tray assembly 139. One example of controllingthe liquid level in the melt tray assembly 139 is described in theapplication entitled “A Method and System of Maintaining a Liquid Levelin a Distillation Tower” (U.S. Ser. No. 61/912,959) by Jaime Valenciaand filed on the same day as the instant application.

It is important to note that the steps depicted in FIG. 8 are providedfor illustrative purposes only and a particular step may not be requiredto perform the inventive methodology. The claims, and only the claims,define the inventive system and methodology.

Disclosed aspects may be used in hydrocarbon management activities. Asused herein, “hydrocarbon management” or “managing hydrocarbons”includes hydrocarbon extraction, hydrocarbon production, hydrocarbonexploration, identifying potential hydrocarbon resources, identifyingwell locations, determining well injection and/or extraction rates,identifying reservoir connectivity, acquiring, disposing of and/orabandoning hydrocarbon resources, reviewing prior hydrocarbon managementdecisions, and any other hydrocarbon-related acts or activities. Theterm “hydrocarbon management” is also used for the injection or storageof hydrocarbons or CO₂, for example the sequestration of CO₂, such asreservoir evaluation, development planning, and reservoir management.The disclosed methodologies and techniques may be used in extractinghydrocarbons from a subsurface region and processing the hydrocarbons.Hydrocarbons and contaminants may be extracted from a reservoir andprocessed. The hydrocarbons and contaminants may be processed, forexample, in the distillation tower previously described. After thehydrocarbons and contaminants are processed, the hydrocarbons may beextracted from the processor, such as the distillation tower, andproduced. The contaminants may be discharged into the Earth, etc. Forexample, as shown in FIG. 8, the method for producing hydrocarbons mayalso include removing 505 the hydrocarbon-enriched vapor stream from thedistillation tower; and producing 506 the hydrocarbon-enriched vaporstream extracted from the distillation tower. The initial hydrocarbonextraction from the reservoir may be accomplished by drilling a wellusing hydrocarbon drilling equipment. The equipment and techniques usedto drill a well and/or extract these hydrocarbons are well known bythose skilled in the relevant art. Other hydrocarbon extractionactivities and, more generally, other hydrocarbon management activities,may be performed according to known principles.

As utilized herein, the terms “approximately,” “about,” “substantially,”and similar terms are intended to have a broad meaning in harmony withthe common and accepted usage by those of ordinary skill in the art towhich the subject matter of this disclosure pertains. It should beunderstood by those of skill in the art who review this disclosure thatthese terms are intended to allow a description of certain featuresdescribed and claimed without restricting the scope of these features tothe precise numeral ranges provided. Accordingly, these terms should beinterpreted as indicating that insubstantial or inconsequentialmodifications or alterations of the subject matter described areconsidered to be within the scope of the disclosure.

For the purpose of this disclosure, the term “coupled” means the joiningof two members directly or indirectly to one another. Such joining maybe stationary or moveable in nature. Such joining may be achieved withthe two members or the two members and any additional intermediatemembers being integrally formed as a single unitary body with oneanother or with the two members or the two members and any additionalintermediate members being attached to one another. Such joining may bepermanent in nature or may be removable or releasable in nature.

It should be understood that numerous changes, modifications, andalternatives to the preceding disclosure can be made without departingfrom the scope of the disclosure. The preceding description, therefore,is not meant to limit the scope of the disclosure. Rather, the scope ofthe disclosure is to be determined only by the appended claims and theirequivalents. It is also contemplated that structures and features in thepresent examples can be altered, rearranged, substituted, deleted,duplicated, combined, or added to each other.

The articles “the”, “a” and “an” are not necessarily limited to meanonly one, but rather are inclusive and open ended so as to include,optionally, multiple such elements.

What is claimed is:
 1. A method for separating a feed stream in adistillation tower comprising: providing a distillation tower comprisinga stripper section and a controlled freeze zone section, wherein thecontrolled freeze zone section comprises a lower section and an uppersection, and wherein the controlled freeze zone section comprises a melttray assembly in the lower section of the controlled freeze zonesection; introducing a feed stream into one of the stripper section andthe controlled freeze zone section of the distillation tower, the feedstream comprising a hydrocarbon and a contaminant; separating the feedstream in the stripper section into an enriched contaminant bottomliquid stream, comprising the contaminant, and a freezing zone vaporstream, comprising the hydrocarbon, at a temperature and pressure atwhich no solid forms; contacting the freezing zone vapor stream in thecontrolled freeze zone section with a freezing zone liquid stream,comprising the hydrocarbon, at a temperature and pressure at which asolid, comprising the contaminant, and a hydrocarbon-enriched vaporstream, comprising the hydrocarbon, form; directly applying heat to acontrolled freeze zone vertical wall of the controlled freeze zonesection with a heating mechanism coupled to at least one of a controlledfreeze zone internal surface of the controlled freeze zone vertical walland a controlled freeze zone external surface of the controlled freezezone vertical wall, wherein the heating mechanism is coupled to thecontrolled freeze zone vertical wall above the melt tray assembly; andat least one of destabilizing and preventing adhesion of the solid tothe controlled freeze zone vertical wall with the heating mechanism. 2.The method of claim 1, wherein applying heat includes heating separatesections of the controlled freeze zone vertical wall with the heatingmechanism.
 3. The method of claim 1, wherein applying heat includesheating the upper section of the controlled freeze zone section.
 4. Themethod of claim 1, wherein the heating mechanism comprises one of (a) acoil containing a fluid and (b) an electrical conductor.
 5. The methodof claim 1, further comprising detecting a temperature of the heatingmechanism with a temperature sensor that is adjacent to the heatingmechanism and coupled to at least one of the controlled freeze zoneinternal surface and the controlled freeze zone external surface.
 6. Themethod of claim 1, further comprising melting or vaporizing the solid inthe upper section of the controlled freeze zone section.
 7. The methodof claim 6, wherein the lower section of the controlled freeze zonesection directly abuts and is separate from the upper section of thecontrolled freeze zone section and wherein the upper section of thecontrolled freeze zone section directly abuts and is separate from thelower section of the controlled freeze zone section.
 8. The method ofclaim 1, further comprising producing the freezing zone liquid stream ina rectifier section of the distillation tower at a temperature andpressure at which substantially no solid forms.
 9. The method of claim8, wherein the distillation tower further comprises a rectifier section,and wherein at least one of the stripping section, the controlled freezezone section, and the rectifier section are in a first vessel andanother of the at least one of the stripping section, the controlledfreeze zone section, and the rectifier section are in a second vesselthat is separate from the first vessel.
 10. A distillation tower thatseparates a contaminant in a feed stream from a hydrocarbon in the feedstream, the distillation tower comprising: a stripper sectionconstructed and arranged to separate a feed stream, comprising acontaminant and a hydrocarbon, into an enriched contaminant bottomliquid stream, comprising the contaminant, and a freezing zone vaporstream, comprising the hydrocarbon, at a temperature and pressure atwhich no solids form; and a controlled freeze zone section constructedand arranged to receive the freezing zone vapor stream from the strippersection and to contact the freezing zone vapor stream with a freezingzone liquid stream at a temperature and pressure at which the a solid,comprising the contaminant, is formed; wherein the controlled freezezone section comprises a lower section and an upper section, where theupper section directly abuts and is separate from the lower section, andwherein the controlled freeze zone section further comprises: a melttray assembly in the lower section of the controlled freeze zone sectionthat is constructed and arranged to melt a solid, comprising thecontaminant, formed in the controlled freeze zone section; a heatingmechanism coupled to at least one of a controlled freeze zone internalsurface of a controlled freeze zone vertical wall of the controlledfreeze zone section and a controlled freeze zone external surface of thecontrolled freeze zone vertical wall that at least one of destabilizesand prevents adhesion of the solid to the controlled freeze zonevertical wall, wherein the heating mechanism is above the melt trayassembly and is in the upper section of the controlled freeze zonesection.
 11. The distillation tower of claim 10, wherein the heatingmechanism comprises one of (a) a coil containing a fluid and (b) anelectrical conductor, and wherein the distillation tower furthercomprises a temperature sensor adjacent to the heating mechanism andcoupled to the controlled freeze zone internal surface or the controlledfreeze zone external surface.
 12. The distillation tower of claim 10,wherein the heating mechanism extends around an internal circumferenceof the controlled freeze zone internal surface or an externalcircumference of the controlled freeze zone external surface.
 13. Thedistillation tower of claim 10, wherein the heating mechanism comprisesa plurality of heating mechanisms, wherein each of the heatingmechanisms is coupled to one of the controlled freeze zone internalsurface and the controlled freeze zone external surface.
 14. Thedistillation tower of claim 10, wherein the heating mechanism comprisesa plurality of heating mechanisms and wherein at least one of theplurality of heating mechanisms is connected to another one of theplurality of heating mechanism.
 15. The distillation tower of claim 10,further comprising a rectifier section constructed and arranged tooperate at a temperature and pressure at which substantially no solidforms.
 16. The distillation tower of claim 15, wherein at least one ofthe stripping section, the controlled freeze zone section, and therectifier section are in a first vessel and another of the at least oneof the stripping section, the controlled freeze zone section, and therectifier section are in a second vessel that is separate from the firstvessel.
 17. The distillation tower of claim 16, wherein the strippingsection and the controlled freeze zone section are in the first vesseland the rectifier section is in the second vessel that is separate fromthe first vessel.
 18. A method for producing hydrocarbons comprising:extracting a feed stream comprising a hydrocarbon and a contaminant froma reservoir; introducing the feed stream into one of a stripper sectionand a controlled freeze zone section of a distillation tower; separatingthe feed stream in the stripper section into an enriched contaminantbottom liquid stream, comprising the contaminant, and a freezing zonevapor stream, comprising the hydrocarbon, at a temperature and pressureat which no solid forms; contacting the freezing zone vapor stream inthe controlled freeze zone section with a freezing zone liquid stream,comprising the hydrocarbon, at a temperature and pressure at which thefreezing zone vapor stream forms a solid, comprising the contaminant,and a hydrocarbon-enriched vapor stream, comprising the hydrocarbon;accumulating at least a portion of the freezing zone liquid stream in amelt tray assembly in the controlled freeze zone section; directlyapplying heat to a controlled freeze zone vertical wall of thecontrolled freeze zone section with a heating mechanism coupled to atleast one of a controlled freeze zone internal surface of the controlledfreeze zone vertical wall and a controlled freeze zone external surfaceof the controlled freeze zone vertical wall, wherein the heatingmechanism is coupled to the controlled freeze zone vertical wall abovethe melt tray assembly; at least one of destabilizing and preventingadhesion of the solid to the controlled freeze zone vertical wall withthe heating mechanism; removing the hydrocarbon-enriched vapor streamfrom the distillation tower; and producing the hydrocarbon-enrichedvapor stream extracted from the distillation tower.
 19. The method ofclaim 18, wherein the heating mechanism comprises a plurality of heatingmechanism and wherein applying heat includes heating separate sectionsof the controlled freeze zone vertical wall with the heating mechanisms.20. The method of claim 18, wherein applying heat includes heating theupper section of the controlled freeze zone section.
 21. The method ofclaim 18, wherein the heating mechanism comprises one of (a) a coilcontaining a fluid and (b) an electrical conductor.
 22. The method ofclaim 18, further comprising detecting a temperature of the heatingmechanism with a temperature sensor that is adjacent to the heatingmechanism and coupled to at least one of the controlled freeze zoneinternal surface and the controlled freeze zone external surface. 23.The method of claim 18, further comprising melting or vaporizing thesolid at in at least one of a lower section of the controlled freezezone section and an upper section of the controlled freeze zone section.24. The method of claim 23, wherein applying heat includes heating theat least one of the lower section and the upper section of thecontrolled freeze zone section, wherein the lower section directly abutsand is separate from the upper section of the controlled freeze zonesection and wherein the upper section directly abuts and is separatefrom the lower section of the controlled freeze zone section.
 25. Themethod of claim 18, further comprising producing the freezing zoneliquid stream in a rectifier section of the distillation tower at atemperature and pressure at which substantially no solid forms.
 26. Themethod of claim 25, wherein at least one of the stripping section, thecontrolled freeze zone section and the rectifier section are in a firstvessel and another of the at least one of the stripping section, thecontrolled freeze zone section and the rectifier section are in a secondvessel that is separate from the first vessel.